Hello all! I got into pipe smoking about a week or two ago. I did some research before hand, so I have a rather basic idea of how to pack, light, tamper, etc. etc. I'm currently using a Dr. Grabow Grand Duke. I smoke Sir Walter out of it. My question pertains to the pipe filter. The one you see sticking out of the stem when you pull it apart from the bowl. I clean my pipe stem after each use, and run a pipe cleaner through it several times. In my research I never once saw anything dealing with Pipe filters. Ive noticed my 'Duke has a pretty nasty filter as of late. Tobacco strands sticking out, and that kind of thing. Is this normal? Is there a 'shelf-life on a filter? Finally, should I be expected to replace a filter after years of smoking? Thanks for any and all help!